I just got attracted by the castings; Lee Dong-Wook as a psychopath in the cover of a normal handsome dentist and Yoon Jong-Woo, a simple country youth looking for progress in life, very calm outside but there is a dragon inside :)) I just felt well-connected to the characters and kept trying to put myself in their positions and think about "what would you do now?" but the story itself, the whole process and how things happen one after another is not an advantage though; that's why I gave 4 outa 5!
In conclusion if you do have interest in mysterious guys or
enjoy watching enigmatic stories about serial killers and how they act or think "Strangers from hell" could be a fitting.